storage: flash_map: handle disabled flash nodes

Don't fail to compile when `fixed-partition`'s exist on a flash device
that is disabled. This does not fix the case where a `fixed-partition`
is on a flash device with `status = "okay"` but with no driver compiled
in.

Signed-off-by: Jordan Yates <jordan.yates@data61.csiro.au>
2 files changed